1. Field of the Invention
The present invention relates to antennas. More specifically, the present invention relates to millimeter wave reflect array antennas and arrays thereof.
2. Description of the Related Art
As noted by the Institute of Electrical and Electronic Engineers (IEEE): “The millimeter-wave region of the electromagnetic spectrum is usually considered to be the range of wavelengths from 10 millimeters (0.4 inches) to 1 millimeter (0.04 inches). This means they are larger than infrared waves or x-rays, for example, but smaller than radio waves or microwaves. The millimeter-wave region of the electromagnetic spectrum corresponds to radio band frequencies of 30 GHz to 300 GHz and is sometimes called the Extremely High Frequency (EHF) range. The high frequency of millimeters waves as well as their propagation characteristics (that is, the ways they change or interact with the atmosphere as they travel) make them useful for a variety of applications including transmitting large amounts of computer data, cellular communications, and radar.” See http://www.ieee-virtual-museum.org/collection/tech.php?id=2345917&lid=1.
For current more demanding applications, such as ‘active denial’, higher power millimeter waves, i.e. waves in the range of tens to thousands of watts, are required. Prior attempts to produce high power millimeter wave energy with solid-state devices have included waveguide and microstrip power combining. At millimeter wave frequencies, this method of combining typically produces unsatisfactory results due to heavy losses in the waveguide and/or microstrip medium.
Another approach involves the use of a spatial array. This approach has shown some promise. However, spatial arrays have not yet produced the power density levels that are required for the more demanding applications mentioned above.
One current approach involves the use of a reflect array amplifier. The reflect array has unit cells, each containing its own input antenna, power amplifier, and output antenna. These unit cells are then configured into an array of arbitrary size. Reflect arrays overcome feed losses by feeding each element via a nearly lossless free-space transmission path.
As disclosed and claimed in U.S. patent application entitled REFLECTIVE AND TRANSMISSIVE MODE MONOLITHIC MILLIMETER WAVE ARRAY SYSTEM AND IN-LINE AMPLIFIER USING SAME, filed Dec. 12, 2003 by K. Brown et al. (10/734445), the teachings of which are hereby incorporated herein by reference, reflect arrays differ from conventional arrays in that the input signal is delivered to the face of the array via free space, generally from a small horn antenna.
An active reflect array consists of a large number of unit cells arranged in a periodic pattern. Each reflect array element is equipped with two orthogonally-polarized antennas, one for reception and one for transmission, and an amplifier therebetween. That is, reflect arrays typically receive one linear polarization and radiate the orthogonal polarization, i.e., the receive antenna receives only vertically-polarized radiation and the transmit antenna transmits only horizontally-polarized radiation.
When integrated with the power-generating electronics on a thin semiconductor substrate, such antennas tend to have narrow bandwidths and high losses due to large surface currents. The size of each unit cell is constrained by the need to avoid grating lobes. For a fixed array with a main beam in the broadside direction, each unit cell may be no more than approximately 0.8 wavelengths on a side typically.
Higher power levels are attained by combining the outputs of multiple transistors. The drawback of this approach is that the power combiners themselves take up valuable area on the semiconductor wafer that could otherwise be occupied by power-generating circuitry.
Consequently, there was a need in the art for an improved system or method for generating a high power millimeter wave beam. Specifically, there was a need for a reflect array antenna capable of generating high power millimeter wave energy without significant loss.
The need was addressed by copending U.S. patent application Ser. No. 11/508,086 entitled AMPLIFIED PATCH ANTENNA REFLECT ARRAY, filed 22 Aug. 2006 by K. W. Brown the teachings of which are hereby incorporated by reference herein. Although this design addresses the need in the art, the array requires high current levels due to the parallel orientation of the amplifier columns in the array with respect to the direct current feed thereof. With multiple parallel columns in the array and potentially multiple chips, thousands of amps of DC current may be required. This requires high current cabling and tends to be lossy. This translates to higher power requirements, higher costs and more bulky arrays.
Hence, a need remains in the art for further improvements systems and methods for generating high power millimeter wave beams. Specifically, a need remains for a reflect array antenna capable of generating high power millimeter wave energy with minimal DC current requirements.